Deuteronomy 19:4-5

⁴"This is the provision for the manslayer, who by fleeing there may save his life. If any one kills his neighbor unintentionally without having been at enmity with him in time past-- ⁵as when a man goes into the forest with his neighbor to cut wood, and his hand swings the axe to cut down a tree, and the head slips from the handle and strikes his neighbor so that he dies--he may flee to one of these cities and save his life;